1. Field of the Invention
The present invention relates to a method used in a wireless communication system and related communication device, and more particularly, to a method of transmitting a multicast signal and a unicast signal simultaneously and related communication device.
2. Description of the Prior Art
A long-term evolution (LTE) system supporting the 3GPP Rel-8 standard and/or the 3GPP Rel-9 standard are developed by the 3rd Generation Partnership Project (3GPP) as a successor of a universal mobile telecommunications system (UMTS), for further enhancing performance of the UMTS to satisfy increasing needs of users. The LTE system includes a new radio interface and a new radio network architecture that provides a high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, a radio access network known as an evolved universal terrestrial radio access network (E-UTRAN) includes multiple evolved Node-Bs (eNBs) for communicating with multiple user equipments (UEs), and communicating with a core network including a mobility management entity (MME), a serving gateway, etc., for Non-Access Stratum (NAS) control.
A LTE-advanced (LTE-A) system, as its name implies, is an evolution of the LTE system. The LTE-A system targets faster switching between power states, improves performance at the coverage edge of an eNB, and includes advanced techniques, such as carrier aggregation (CA), coordinated multipoint transmission/reception (CoMP), uplink (UL) multiple-input multiple-output (MIMO), etc. For a UE and an eNB to communicate with each other in the LTE-A system, the UE and the eNB must support standards developed for the LTE-A system, such as the 3GPP Rel-10 standard or later versions.
On the other hand, multimedia broadcast multicast service (MBMS) service or evolved MBMS (E-MBMS) service have been introduced in the UMTS, the LTE system and the LTE-A system, for transmitting multicast/broadcast signals such as TV programs, films, music, etc. to user equipments. Comparing with a traditional unicast, the MBMS service (hereafter referred to both the MBMS service and/or the E-MBMS service) is downlink only, and is multicasted/broadcasted from a network of the abovementioned systems to multiple (e.g., a specific group of) UEs via a point-to-multipoint transmission. Characteristic of the MBMS service enables the network to provide the MBMS service to unlimited number of UEs with a constant network load. Besides, a UE in the UMTS, the LTE system and/or the LTE-A system can receive the MBMS service inherently, and no additional hardware component is needed to be installed for the MBMS service. Thus, the MBMS service is attractive considering both hardware cost and resource efficiency.
According to the above description, the network can provide the MBMS service to the UEs by using multiple antennas, to improve the reception of the multicast/broadcast signals. Besides, dedicated radio resource (i.e., MBMS resource) is allocated for transmitting the multicast/broadcast signals carrying the MBMS service, according to the MBMS service currently developed. However, distribution (i.e., locations) of the UEs varies constantly, and there are situations where the network only needs to transmit the multicast/broadcast signals by using part of the antennas. If the rest of the antennas are not exploited, transmission efficiency of the network is wasted. Thus, exploiting part of the antennas for improving the transmission efficiency of the network, to enhance the capacity of the wireless communication system is a topic to be discussed and addressed.